Korean War Project:Comprehensive site regarding the Korean war, that includes message boards (the call them "BBS" sections) broken down by different military divisions. In addition to the boards, the site has a variety of good information and links.
Military.com:User-friendly message board that covers a variety of topics regarding the Korean war. Plus, you can add new topics of your own, if you have a subject you think may be of interest to others.
WWII in Color:Although this board is centered around World War II, there is an entire section on the Korean War. A good place to visit not only for that, but for other related topics that may be worthwhile.
Arm Chair General:Broad military-based forum with a section dedicated to the Korean War. Another message board that can you give you specific discussion platforms, as weel as some more general subjects.
Genealogy.com:Great resource for finding people with whom you or a friend or relative may have lost touch. Although it's a large site, there is a section dedicated solely to researching people from the Korean War.